Method and appliance for supplying fuel to a premixiing burner

ABSTRACT

A method and an appliance are described for supplying fuel to a premixing burner for operating a gas turbine, which premixing burner has at least one burner shell ( 1, 2 ) at least partially bounding an axially extending premixing burner space, having a premixing gas supply directed into the premixing burner space via the burner shell ( 1, 2 ), the premixing gas ( 6 ) being mixed with combustion inlet air and being ignited downstream external to the premixing burner,  
     The invention is characterized by the fact that the premixing gas supply is carried out separately by means of at least two spatially axially separated regions (S 1,  S 2 ) along the burner shell ( 1, 2 ), having a region (S 1 ), which is arranged upstream, and at least a second region (S 2 ), which is arranged downstream, by the fact that more than 60% of the total premixing gas supply takes place via the first region (S 1 ) in order to start the gas turbine, and by the fact that a stepwise or continuous redistribution of the premixing gas supply to the second region (S 2 ) takes place for the further run-up of the load on the gas turbine to full load.

TECHNICAL FIELD

[0001] The invention relates to a method and an appliance for supplying fuel to a premixing burner for operating a gas turbine, which premixing burner has at least one burner shell at least partially bounding an axially extending premixing burner space, having a premixing gas supply directed into the premixing burner space via the burner shell, the premixing gas being mixed with combustion inlet air and being ignited downstream, external to the premixing burner.

PRIOR ART

[0002] Premixing burners of the previously mentioned generic type for the operation of gas turbine installations are sufficiently known and have different premixing burner geometries. As an example, a conical premixing burner consisting of a plurality of burner shells, a so-called double-cone burner, is described in EP 0 321 809 B1. Its burner shells are combined in such a way that tangential air inlet slots for the combustion inlet air are formed along the burner center line. On the burner shell inlet edges formed by this means, outlet openings for the premixing gas, which are arranged with a distribution in the direction of the burner center line, are provided. The injection of the premixing gas through the outlet openings along the burner shell inlet edges of the leads, because of the burner shell geometry, in association with the combustion inlet air, to a swirl-shaped thorough mixing of the premixing gas and the combustion inlet air.

[0003] Another premixing burner geometry is shown in WO 93/17279 in which the premixing burner is configured with an additionally conical inner body. In this case also, the premixing gas is fed into the interior of the premixing burner via corresponding outlet openings, which are arranged along the axially extending air inlet slots, the premixing gas being thoroughly mixed with the combustion inlet air in the interior of the premixing burner and being brought to ignition downstream within the combustion chamber.

[0004] Now, it is possible to undertake optimization with respect to the quality of the combustion by appropriate selection of the arrangement, size and number of the outlet openings and by appropriate selection of their distance apart. As an example, it is particularly possible to influence decisively the emission values, the extinguishing behavior of the flame forming in the combustion chamber, the flame reverse flow behavior and the flame stability by appropriate selection of the parameters mentioned above.

[0005] The optimization possibilities described above rapidly reach their limits, however, where it is desired to take measures to optimize the burner behavior otherwise than in the case of a permanently specified burner geometry and in the case of an ideal combustion condition. In the case of a specified design arrangement of outlet openings along certain regions of the burner shells, for example, it is almost impossible to keep the combustion behavior to an almost constant optimum level in the case of different load and environmental conditions. It has been found that an optimized arrangement of outlet openings for the premixing gas supply within the premixing burner, which has been designed in optimum manner for use in a certain type of machine, for example for use on an annular combustion chamber, can only be utilized inefficiently or at all for use in another machine type, for example for use in a silo combustion chamber.

[0006] In the course of the use of a burner, furthermore, creeping burner system changes occur which are caused by fatigue phenomena and lead, for example, to an increase in leakage airflows. Due to the permanently specified arrangement of the premixing gas passage openings, which themselves are subject to no or only negligible ageing phenomena, however, no compensation can be provided for the changes due to ageing so that a deterioration in the combustion process with increasing operating time of the burner is unavoidable.

[0007] Existing premixing gas supply systems are, as a rule, optimized, with respect to low emission values and damped occurrence of combustion oscillations, for the medium and high load region of gas turbines. Pilot stages are usually employed in order to start the combustion process and attain the medium load range of the gas turbine. Pilot gas is usually fed centrally, relative to the premixing burner center line, into the interior of the premixing burner by means of a burner lance. This pilot gas is mixed with the combustion inlet air and brought to ignition. It is only after a certain load range has been attained that the pilot gas supply is switched off and the premixing gas supply put into operation. Such a switching procedure, in which the premixing gas supply is switched off and the pilot gas supply is switched on, takes place in the same manner when the gas turbine is being run down. A high level of combustion oscillation, however, occurs within the burner system during the switching processes; these are associated with strong pressure fluctuations which in turn involve a direct and disturbing effect on the loading behavior of the gas turbine which, as a consequence, is subjected to large load oscillations.

[0008] If a gas supply system is switched off, during both run-up and run-down of the gas turbine, it is necessary to clean the switched-off gas supply lines with inert gas in order to exclude flash-back in the supply line and to avoid damage to it. The quantity of inert gases necessary for cleaning the gas supply line is substantial and also leads not least to high operating costs for such burner systems.

[0009] Finally, it is almost impossible—using the currently known premixing burners—to operate the premixing burner with different types of fuel such as, for example, liquid or gaseous fuel, particularly because the burner lance for the supply of pilot gas, which is usually arranged centrally in the burner center line (this pilot gas being necessary, as previously mentioned, for running up the gas turbine and for the lower load range), is arranged in the direct spatial vicinity of the central liquid fuel nozzle. It is impossible to exclude undesired ignition interaction between the two fuel outlets.

PRESENTATION OF THE INVENTION

[0010] The invention is based on the object of further developing a method and an appliance for the fuel supply to a premixing burner, as described in the preamble to claim 1 and the preamble to claim 8, in such a way that the disadvantages of the prior art, as listed above, may be avoided. In particular, measures should be taken at the premixing burner so that an optimized adaptation of the premixing burner behavior is made possible over the complete load range of the gas turbine. This should, in particular, take place without large-scale technical and design complication and so that it can be realized at only small cost.

[0011] The solution to the object on which the invention is based is given in claim 1 and claim 8. Features advantageously developing the concept of the invention are the subject matter of the subclaims and the description and are, in particular, to be extracted with reference to the figures.

[0012] The idea on which the invention is based is the axially staged supply of premixing gas along the flanks of the burner shells, the burner shells being subdivided into at least two regions arranged axially one behind the other, which regions are respectively supplied by means of premixing gas supply lines conducted separately from one another. The regions separated from one another along the burner shells are arranged axially one behind the another in the flow direction of the premixing burner, it being recognized, according to the invention, that in order to start the gas turbine, more than 60% of the total premixing gas supply should take place via the upstream first region and the a stepwise or continuous redistribution of the premixing gas supply to the downstream regions adjacent to the first region takes place for the further run-up of the load of the gas turbine to full load.

[0013] The axial subdivision of the premixing gas supply along the burner shells of the premixing burner and, in particular, the stepwise supply of the individual regions with premixing gas makes it possible to dispense completely with the supply of pilot gas, even in the case of starting and in the lower load regions of the gas turbine.

[0014] A number of advantages which not least follow from the disappearance of the combustion chamber oscillations associated with the switching from pilot gas to a premixing gas supply are associated with the possibility of dispensing with a pilot gas stage. The mode of operation of the premixing burner according to the invention makes it possible, for the first time, to operate a gas turbine from starting to full load without a pilot gas stage. The continuous or stepwise switching-on of individual regions, via which the premixing gas can pass to the interior of the premixing burner, takes place with the aid of open-chain or closed-loop control units provided in the individual supply lines. In the simplest case, these units are configured as controllable throttle valves.

[0015] Advantageously dispensing with a pilot gas supply makes it possible, in particular, to atomize liquid fuel by means of a central injection nozzle penetrating into the mouth of the burner, which liquid fuel is in turn surrounded, in an appropriate manner, by a tubular configuration of combustion airflow.

[0016] An embodiment configured according to the invention for the targeted supply-flow control of premixing gas for the premixing burner shells, which are subdivided into different regions, is indicated in the following description, with reference to the figures. Essential aspects of the method according to the invention and of the appliance described in detail below is the separate, metered premixing gas supply to the individual regions, arranged axially one behind the other, along the burner shells, by means of which the premixing gas is injected into the interior of the premixing burner.

BRIEF DESCRIPTION OF THE INVENTION

[0017] The invention is described as an example below, without limitation to the general idea of the invention, using exemplary embodiments and with reference to the drawing. In the drawing:

[0018]FIG. 1 shows a diagrammatic, cross-sectional representation through a premixing burner with a conical configuration,

[0019]FIG. 2 shows a diagrammatic representation relating to the mode of operation of the exemplary embodiment represented in FIG. 1,

[0020]FIG. 3 shows a diagrammatic plan relating to the run of supply lines for the supply of premixing gas to the premixing burner,

[0021]FIG. 4 shows a exemplary embodiment of a control valve.

WAYS OF IMPLEMENTING THE INVENTION, COMMERCIAL APPLICABILITY

[0022]FIG. 1 presents a diagrammatic representation of a longitudinal section through a premixing burner with a conical configuration. The premixing burner has conically configured burner shells 1, 2, along which outlet openings 3 are provided in the axial direction relative to the burner longitudinal center line A, through which outlet openings 3 premixing gas can be fed into the interior of the premixing burner. The burner shells 1, 2 are subdivided into two differently separated regions Stage S1, Stage S2, which are supplied with premixing gas by different premixing gas supply lines 4, 5. Inlet air is guided into the interior of the premixing burner through air inlet slots (not represented in FIG. 1) likewise tangentially in the direction of the conical shape and is blended with the premixing gas 6 to form a fuel/air mixture.

[0023] A liquid fuel atomization direction 7, which permits a mixed operation or a switch-over from gaseous fuel to liquid fuel, can be optionally provided in the center of the premixing burner. The supply of liquid fuel takes place by means of an atomization nozzle, known per se, which generates a conically propagating atomization cloud within the premixing burner. For protection relative to the premixing outlet openings 3 and for shape stabilization purposes, the propagating liquid fuel cloud is surrounded by a protective air shroud.

[0024] No predoping, as is usual in the prior art, is undertaken in order to start the gas turbine, i.e. in order to ignite the premixing burner, but, [lacuna] two-stage premixing burner unit represented in the exemplary embodiment, each region of the burner shell is provided with a premixing gas supply which is arranged upstream within the premixing burner. In the exemplary embodiment, this is the Stage 1 region, which is operated with more than 60% of the total premixing gas supply for starting and for operating the premixing burner in the low 8 load range.

[0025]FIG. 2 shows a general view diagram in which the percentage distribution of the premixing gas subdivision between region S1 and region S2 can be seen. The fields shown in black correspond to the proportion of the premixing gas emerging via the region 1, the lighter fields respectively showing the premixing gas proportion which passes into the interior of the burner via the region S2 of the premixing burner. As already mentioned above, the lion's share, i.e. more than 90%, of the total premixing gas supply flows via the region 1 into the interior of the premixing burner during ignition. In the lower load region (idle), the proportion of the premixing gas emerging via the region 2 increases slightly. In the case of the half-load condition, the two regions S1 and S2 are supplied with approximately equal parts of premixing gas. During full-load operation, rather more premixing gas passes into the interior of the premixing burner via the region S2 than via the region 1. The premixing gas allocation to the regions S1 and S2, as represented in FIG. 2, takes place by means of a control unit, which can undertake, stepwise or continuously, the distribution ratio for the premixing gas allocation to the regions S1 and S2. In the simplest case, these are coupled throttle valves, which are respectively provided in the individual supply lines 4 and 5.

[0026] A further possibility for the controlled premixing gas supply to the separated regions of the premixing burner can be seen in the diagrammatic representation of FIG. 3. The exemplary embodiment of FIG. 3 again involves a conical premixing burner, which has available two regions S1 and S2, by means of which separated premixing gas enters the interior of the premixing burner. In a common supply line 8, by means of which premixing gas is supplied to the premixing burner, a main control valve 9 is provided. The direct supply of premixing gas to the region S1 of the premixing burner can be controlled by means of the main control valve 9. A crossing point 10, at which part of the premixing gas can be diverted into a supply branch 11, is provided in the supply line between the main control valve 9 and the outlet region S1 of the premixing burner. A further control unit in the form of an overpressure valve 12, which is subjected to spring force and which is described in more detail below with reference to FIG. 4, is provided in the supply branch 11. A bypass line 13, whose flow cross section is small enough, or within which a corresponding throttling element 14 is provided, ensures that a small premixing gas flow can be supplied to the region S2 of the premixing burner when the control valve 12 is closed.

[0027] The supply system for premixing gas to the two regions S1 and S2 of the premixing burner, as represented in FIG. 3, has the following mode of operation. After the main control valve 9 has been opened, the region S1 of the premixing burner is supplied with premixing gas. The gas pressure within the supply lines supplying the region S1 with premixing gas, and also in the supply line 11, is not yet capable of opening the overpressure valve, which is subjected to spring force. Only a small proportion of the premixing gas passes via the bypass line 13 to the region S2 of the premixing burner and there emerges into the interior of the premixing burner. This corresponds to the condition when starting the gas turbine or when igniting the premixing burner. After the starting phase, the premixing gas pressure present in the supply line 11 increases. This premixing gas pressure is capable of continuously opening the throttle valve 12, which is subjected to spring force, so that a continually increasing proportion of the premixing gas flowing through the main control valve 9 flows through the overpressure valve 12 into the region S2. If the supply line gas pressure increases further, the overpressure valve 12 opens completely so that a large proportion of the premixing gas can pass into the region S2 of the premixing burner. It is possible to optimize the behavior of the premixing burner with respect to emissions and oscillation behavior by the dimensioning of the supply lines and by the setting of the demand behavior of the overpressure valve 13. By this means, it is possible to realize a premixing burner for operating a gas turbine over the whole of the load range without the necessity for a pilot gas supply and while using only one single control valve, namely the overpressure valve 12.

[0028] Such an overpressure valve is represented as an advantageous embodiment in FIG. 4. The overpressure valve 12 has a conically configured piston 15 which, subjected to spring force by a spring 16, is in gas-tight contact with a mating contour 17. If the piston 15 is subjected to pressure by means of gas pressure (on this point, see arrow on the left-hand side of the throttle valve), the gas pressure acting on the piston 15 is capable of compressing the spring 16 against a stop 18. In this process, a gap opens between the piston 15 and the mating contour 17, so that gas can penetrate to the right through the overpressure valve. Depending on the selection of the spring force of the spring element 16 and the dimensioning of the piston size, the premixing gas flow rate through the overpressure valve 12, which depends on gas pressure, can be individually set. With the aid of appropriate dimensioning of the overpressure valve 12 and the supply lines 11 and 14 participating in the premixing gas supply, it is possible to optimize the combustion process in a manner known per se. In the case of the embodiment example represented in FIG. 3, it is also possible to obtain a specified premixing gas distribution between Stages S1 and S2 of the burner shells of the premixing burner according to the representation in the diagram of FIG. 2.

[0029] A number of disadvantages are associated with the method and appliance, according to the invention, for the supply of fuel to a premixing burner. Due to the stepped premixing gas supply into the premixing burner, the latter can be employed within the significantly larger range limits as compared with premixing burners which are designed with only one stage.

[0030] Only one single premixing gas supply line is necessary using the embodiment represented in FIG. 3.

[0031] Due to the use of a control unit configured as an overpressure valve, only one single control unit is necessary for operating the premixing burner.

[0032] The retrofitting of the method according to the invention on already existing premixing burner systems can be easily carried out, in particular because the use of two or more separate premixing gas supply systems is unnecessary.

[0033] Due to the targeted supply of a minimum proportion of premixing gas into the second region of the premixing burner via the bypass line, it is not necessary to clean this supply line with natural gas. Tests have shown that the system according to the invention only causes slight pulsations in the starting behavior. By means of the individual premixing gas distribution to the different regions of the premixing burner, it is possible to undertake corresponding optimization procedures even in the case where ageing phenomena appear.

[0034] Because it is possible to dispense with a pilot gas supply, any pulsations which occur when switching between pilot gas and premixing gas supply can be avoided.

[0035] The complete appliance is simple in design and can be manufactured at favorable cost.

[0036] List of Designations 1, 2 Burner shells  3 Premixing gas outlet openings 4, 5 Supply lines  6 Premixing gas  7 Liquid fuel atomization device  8 Supply line  9 Main control unit 10 Crossing point 11 Branch line 12 Overpressure valve 13 Bypass line 14 Throttle element 15 Piston 16 Spring 17 Mating contour 18 Stop S1, S2 Regions 1, 2 for the staged premixing gas outlet 

1. A method for supplying fuel to a premixing burner for operating a gas turbine, which premixing burner has at least one burner shell (1, 2) at least partially bounding an axially extending premixing burner space, having a premixing gas supply (3) directed into the premixing burner space via the burner shell (1, 2), the premixing gas (6) being mixed with combustion inlet air and being ignited downstream, external to the premixing burner, characterized in that the premixing gas supply is carried out separately by means of at least two spatially axially separated regions (S1, S2) along the burner shell (1, 2), having a region (S1), which is arranged upstream, and at least a second region (S2), which is arranged downstream, in that more than 60% of the total premixing gas supply takes place via the first region (S1) in order to start the gas turbine, and in that a stepwise or continuous redistribution of the premixing gas supply to the second region (S2) takes place for the further run-up of the load on the gas turbine to full load.
 2. The method as claimed in claim 1, characterized in that the supply of the premixing gas to the first region (S1) and the second region (S2) takes place mutually independently.
 3. The method as claimed in claim 1 or 2, characterized in that, under full-load conditions, at least 50% of the total premixing gas supplied to the premixing burner is supplied via the second region (S2) or the regions located downstream.
 4. The method as claimed in one of claims 1 to 3, characterized in that the premixing burner is conically configured and has at least two burner shells (1, 2), which are arranged relative to one another in such a way that they respectively bound two air inlet slots through which the combustion air enters the conically widening premixing burner space, in that the first region (S1) of the burner shells (1, 2), via which at least part of the premixing gas is fed into the premixing burner space, is arranged in the region of the narrowest conical cross section and extends into the premixing burner region which is widening in cross section.
 5. The method as claimed in one of claims 1 to 4, characterized in that the regions, which are axially separated from one another, for the supply of premixing gas are supplied with premixing gas via separate supply lines.
 6. The method as claimed in one of claims 1 to 5, characterized in that the premixing gas supply to the individual regions takes place mutually independently.
 7. The method as claimed in one of claims 1 to 5, characterized in that the premixing gas supply to the individual regions is carried out by means of a single control unit (12).
 8. An appliance for supplying fuel to a premixing burner for operating a gas turbine, which premixing burner has at least one burner shell (1, 2) at least partially bounding an axially extending premixing burner space, having a premixing gas supply directed into the premixing burner space via the burner shell (1, 2), the premixing gas (6) being mixed with combustion inlet air within the premixing burner and being ignited downstream, external to the premixing burner, characterized in that at least two spatially separated regions (S1, S2) are provided axially along the burner shell (1, 2), via which regions (S1, S2) premixing gas (6) can be fed into the premixing burner space and which are connected by means of separate premixing gas supply lines (4, 5), and in that a closed-loop or open-chain control unit (12) is provided, which is connected to the premixing gas supply lines (4, 5) and distributes the premixing gas supply to the individual regions as a function of the load range of the gas turbine.
 9. The appliance as claimed in claim 8, characterized in that a first region (S1) is provided in the burner shell (1, 2), which first region (S1) is arranged upstream in the premixing burner, and in that at least a second region (S2) is arranged, which is arranged downstream of the first region (S1) in the premixing burner.
 10. The appliance as claimed in claim 8 or 9, characterized in that the first region (S1) is connected to a premixing gas supply line in which a throttle valve (9) is provided, in that a crossing point (10) is provided between the throttle valve (9) and the first region (S1), from which crossing point (10) a supply line (11) leads to the second region (S2), and in that the closed-loop or open-chain control unit (12) is provided between the crossing point (10) and the second region (S2).
 11. The appliance as claimed in claim 10, characterized in that the closed-loop or open-chain control unit is an overpressure valve which is subject to spring force.
 12. The appliance as claimed in claim 10 or 11, characterized in that a bypass line (13) is provided between the crossing point (10) and the second region (S2), which bypass line (13) ensures a minimum supply of premixing gas (6) to the second region (S2) provided that the first region (S1) is supplied with premixing gas (6). 